1. Field of the Invention
The present invention relates to grippers for gripping a workpiece.
2. Description of the Related Art
Grippers are mechanical devices characterized by one or more jaws that move together or apart by motive force typically from an electric motor or pneumatic piston. Once moved into a position of contact with the gripped workpiece, the jaws produce a gripping force against the workpiece. It is often desirable for the gripper to provide as large a gripping force as possible while also possessing a minimum weight and physical size. Typically, increasing gripping force increases the size of the motor or piston which increases the weight and physical size of the gripper.
By it's nature, operation of a gripper involves two distinct actions. The jaws must first be moved into a position of contact with the workpiece, after which, the jaws apply a force against the workpiece sufficient to affect subsequent movement (e.g., lifting) of the workpiece. Moving the jaws to the workpiece requires each jaw to exert enough force to overcome the mass inertia of any tooling attached to the jaw and any friction between the jaw and the surfaces of the gripper body that support and guide the jaw. The second action requires each jaw to exert the full intended grip force against the workpiece. While gripping, the jaws must only move sufficiently to compensate for any compliancy from the workpiece or tooling to maintain gripping contact. In other words, the actions of the gripper are separable into two regimes; the first being the jaws traveling some distance with low force until contact is made; and the second is the jaws applying high force against the object.